Optical flow is a measure of image movement across a visual field. It is the apparent motion of image brightness patterns in a sequence of images. In an image each pixel corresponds to the value obtained by the projection of a three-dimensional image onto an image plane. When an object moves, the corresponding projection, or image element within the image data corresponding to object, changes position in the image plane. Optical flow is the vector field showing the direction and magnitude of such changes from one image to the other.
In conventional stereo vision based collision avoidance approaches, the actual distance to a remote object is calculated. However, such distance measurements may be difficult in changing environmental conditions. Hence, an improved collision warning system would not necessarily determine the actual distance to a remote object.